Laser cutting nozzle for a laser machining unit and method for operating such a laser machining unit

ABSTRACT

A laser cutting nozzle for a laser machining unit is described, the nozzle including a passage for the laser beam and cutting gas. The passage extends between a nozzle inlet and a nozzle mouth along a passage longitudinal axis. The passage comprises a convergence portion and a divergence portion. In the entire divergence portion, the wall of the passage forms an angle of inclination relative to the passage longitudinal axis of at most 5°. In addition, the length of the divergence portion is less than 5 times the diameter of the constriction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority under 35U.S.C. § 120 from PCT Application No. PCT/EP2016/074549 filed on Oct.13, 2016, the entire contents of which is incorporated herein byreference.

TECHNICAL FIELD

The invention relates to a laser cutting nozzle for a laser machiningunit.

BACKGROUND

Modern laser machining units are generally able to deliver flawlesscutting results at high machining speeds. Said units encounterlimitations, however, when machining complex three-dimensionalworkpieces. For example, parameters that determine the cutting process,such as the nozzle-workpiece distance, the position of the laser nozzle,etc., may not be able to be kept sufficiently constant or setsufficiently precisely owing to unfavorable spatial configurations.Quality losses may thus occur in the case of cutting work in corners orat angles of a workpiece, leading for example to increased occurrence ofcorrugations or (micro) ridges. Furthermore, the risk of componentcollisions, e.g. owing to workpieces that deviate from the specifiedshape, increases with increasing the machining speed and a small nozzledistance from the workpiece.

It is known from literature that the characteristics of the cutting gasjet emerging from the nozzle have a significant influence on the qualityof the cutting results. For this reason, for shaping the gas jet,nozzles having an inner contour or passage were proposed which, in amanner deviating from nozzles having a simple conical passage, areprovided with a conical-cylindrical, conical-divergent or generally witha convergent-divergent passage. By way of example, reference is made tothe technical article “Design and Characteristic Analysis of SupersonicNozzles for High Gas Pressure Laser Cutting” by H. C. Man et al.,Journal of Materials Processing Technology, Volume 63 (1997), pages217-222.

A laser cutting nozzle of the type mentioned at the outset, comprising aconvergent-divergent passage, is known for example from U.S. Pat. No.6,423,928. Proceeding from a cylindrical constriction portion, the knownnozzle has a marked conical cross-sectional widening in the mouthregion. As a result thereof, the nozzle furthermore comprises just avery narrow end face at the end facing the workpiece, and thesensitivity of the nozzle to capacitive distance control is thereforesuitable only for very small machining distances.

SUMMARY

This document describes a laser machining unit including a passage forthe laser beam and cutting gas, which passage extends between a nozzleinlet and a nozzle mouth, along a passage longitudinal axis, the passageconverging continuously, towards the mouth thereof, in a convergenceportion, as far as a constriction of the passage, to less than 40% ofthe cross-sectional area at the inlet of the convergence portion, thepassage diverging continuously in a divergence portion, proceeding fromthe constriction, as far as the mouth of the passage, to over 130% ofthe cross-sectional area at the constriction.

The invention further relates to a laser machining unit comprising alaser cutting nozzle of this kind, and to a method for operating thelaser machining unit.

The object of the invention is that of providing a laser cutting nozzlethat allows for three-dimensional laser cutting machining having bettercutting results.

Within the meaning of the invention, the wall of theconvergent-divergent passage is at an angle of inclination relative tothe passage longitudinal axis of at most 5°, over the entire divergenceportion, and the length of the divergence portion is less than 5 timesthe diameter of the constriction.

The average angle of inclination of the wall of the passage relative tothe passage longitudinal axis in the divergence portion is preferablyless than 4.0°. In particularly preferred designs of the nozzle, theangle of inclination is even less than 3.0° or less than 2.0°. Inparticular, however, the average angle of inclination is greater than1.0°.

Limiting the angle of inclination to at most 5° in the divergenceportion ensures effective shaping of the emerging gas jet over theentire divergence portion. “Detachment” or “break-off” of the gas flowat the edges, which results in undesired inhomogeneity of the gas flow,is prevented. Despite the relatively small maximum angle of inclination,the divergence portion can be, however, not longer than 5 times thediameter of the constriction. It has surprisingly been found that thislength is sufficient for effective gas jet shaping. In particular, evena length of the divergence portion of less than 4 times or 3 times thediameter of the constriction is sufficient. However, in order to ensurea sufficient effect, the difference portion should preferably be atleast more than twice the diameter of the constriction.

The shaping, according to the invention, of the passage brings aboutconstant fluid dynamic ratios in the gas stream over a large distance,in particular over a region of from 1.5 to 6 mm, after said streamleaves the nozzle, i.e. in particular during machining on the workpiecesurface and in the cutting gap. In this case, the shaping according tothe invention causes the cutting gas to at least reach the speed ofsound and for this to be retained over a long effective distance. Thenozzle is in particular shaped such that the cutting gas already reachesthe speed of sound at the constriction, and is subsequently acceleratedto supersonic speed in the divergent part of the nozzle.

In the case of a preferred embodiment of the invention, the averageangle of inclination of the wall in the convergence portion is greaterthan 5°. Owing to the greater angle of inclination, the convergenceportion can be designed so as to be shorter, with the result that thenozzle as a whole is more compact. In particular, the length of thedivergence portion is advantageously more than 1.4 times and/or lessthan 1.7 times the length of the convergence portion.

The average angle of inclination of the wall in the convergence portionis preferably even greater than 7°. However, in order to preventundesired influences on the gas flow, the average angle of inclinationis in particular less than 15°, preferably even less than 13°.

In a preferred variant of the invention, the convergence portiontransitions directly into the divergence portion at the constriction.The fact that the convergence and divergence portion are in directsuccession makes the desired effect of the increase in the flow speed(preferably to supersonic speed) particularly pronounced. In particular,no cylindrical constriction portion of significant length is providedbetween the convergence and the divergence portion.

Within this meaning, a preferred embodiment is also advantageous inwhich the convergence portion transitions in an edgeless manner and/orgradually into the divergence portion at the constriction. There istherefore no sudden change in the angle of inclination of the wall atthe transition from the convergence portion to the divergence portion.The formation for example of a disadvantageous edge, which may have anundesired influence on the gas flow, is prevented.

Overall, a preferred design of the nozzle is one in which the wall has acontinuous, edge-less course over the entire passage.

In the case of a particularly preferred embodiment, the convergenceportion comprises a wall that is curved towards the passage longitudinalaxis, at least in portions, which wall preferably has a radius ofcurvature of between 4 and 8 mm.

Alternatively or in addition, the divergence portion comprises a wallthat is curved towards the passage longitudinal axis, at least inportions, which wall preferably has a radius of curvature of between 20and 30 mm.

In order to ensure a defined inlet flow, a preferred variant of thenozzle additionally comprises an inflow portion that is arrangedupstream of the convergence portion, on the inlet side. The inflowportion is preferably cylindrical.

In order to ensure cutting characteristics that are independent of thecutting direction, the inflow portion and/or the divergence portionand/or convergence portion preferably have a circular cross section.

A nozzle that is as compact in structure as possible results from thepassage being formed exclusively by a cylindrical inflow portion, theconvergence portion and the divergence portion. In connection with thisaspect, an embodiment is also preferred in which the nozzle is asingle-hole nozzle.

In order to form a homogeneous gas flow even at distances of severalmillimeters from the nozzle mouth, various structural measures have beenfound to be particularly advantageous. For example, the cross-sectionalarea of the mouth should be smaller than the cross-sectional area of theinlet. Said cross-sectional area of the mouth is preferably more than15% and/or less than 75% of the cross-sectional area of the inlet. Thecross-sectional area of the constriction is preferably more than 180%and/or less than 250%, preferably less than 220%, of the cross-sectionalarea of the constriction.

In particular for three-dimensional laser cutting machining ofcomponents, preferably metal profile components, a design of the nozzlehaving the following diameter dimensions is advantageous. Preferably,the diameter of the mouth is between 1.8 and 3.5 mm, the diameter of theconstriction is between 1.3 and 3.0 mm, and/or the diameter of the inletis between 4.0 and 5.0 mm.

In the case of a preferred embodiment, the length of the convergenceportion is between 3.5 and 4.5 mm, the length of the divergence portionis between 5.0 and 7.0 mm, and/or the length of the inflow portion isbetween 1.0 and 1.5 mm.

The outer contour of the laser cutting nozzle plays a particular role inparticular in two respects. Firstly, for use in three-dimensionalworkpiece machining the laser cutting nozzle should be as small aspossible in order that collision-free machining can be ensured even invery restricted space conditions. Furthermore, the laser cutting nozzleis preferably used in conjunction with capacitive nozzle-workpiecedistance control. The outer contour, in particular the surface of thenozzle that is close to the workpiece, can have a decisive influence onthe significance of the capacitance measurement signal for the distancecontrol. Embodiments explained in the following are thereforecharacterized by particular advantages with respect to use of the nozzlein conjunction with capacitive distance control.

The outside diameter of the nozzle on the mouth side is preferablybetween 3.0 and 4.6 mm. Furthermore, the length of a conical peripheralsurface on the mouth side is between 4.0 and 5.0 mm and/or the angle ofinclination of said surface relative to the passage longitudinal axis isbetween 20 and 30°.

A particularly preferred embodiment that is advantageous in terms ofstructure is one in which the outer periphery of the nozzle is greatest,in the longitudinal direction, approximately at the height of theconstriction.

Advantages in terms of handling result from the conical peripheralsurface of the nozzle on the mouth side transitioning into a cylindricalperipheral surface in the region of the nozzle having the largestoutside diameter, which cylindrical peripheral surface is preferablyprovided with a knurling.

In order to fasten the nozzle to a machining head of a laser machiningunit, an external thread is formed on the peripheral surface of thenozzle, at the inlet side. Alternatively, the fastening means may bedesigned in any other manner desired, e.g. by means of annular clampingelements.

It is advantageous, in terms of manufacture and for use in conjunctionwith capacitive distance control, for the nozzle to comprise an integralmain body consisting of metal, preferably copper, the main body formingat least the divergence portion of the passage. In particular, thenozzle is produced integrally from metal, preferably copper.

A nozzle structure comprising an end face that extends perpendicularlyto the passage longitudinal axis and surrounds the mouth is alsoadvantageous for use in conjunction with capacitive distance control. Adesign of the end face, which annularly surrounds the mouth, having awidth of from 0.3 to 0.7 mm has proven expedient in practice. Thisdesign achieves a sufficiently high response characteristic that alsoallows for distance control for large working distances (distancebetween the end face and the workpiece) in the range of over 2 mm, inparticular in the range of up to 6 mm. Machining at a greater workingdistance increases the process reliability, which also makes it possibleto carry out error-free machining at high speeds, at a feed rate in therange of over 10 m/min, in particular even in the range of from 30 to 50m/min.

A laser machining unit comprising a laser cutting nozzle described aboveand in the following is also considered to be part of the invention. Theadvantages of the nozzle design according to the invention result inparticular if the nozzle is used in conjunction with capacitive distancecontrol of the nozzle-workpiece distance, which control determines thecapacitance between the nozzle and the workpiece for the purpose of thecontrol. The unit preferably comprises a machining head that is equippedwith the laser cutting nozzle and is intended for three-dimensionallaser cutting machining.

The unit preferably comprises a CO₂ or solid-state laser, in particulara disc laser, having a maximum power of at least 2 kW, as the lasersource. Alternatively, fiber lasers and laser diodes can also be used.

In order to ensure that the laser beam does not strike the inner wall ofthe nozzle owing to too large a divergence angle, in a preferredembodiment the laser source of the unit can generate a laser beam havinga beam parameter product of ≤8 mm mrad, preferably ≤4 mm mrad, morepreferably ≤2 mm mrad.

Furthermore, a method for operating a laser machining unit using thelaser cutting nozzle described above and in the following is consideredpart of the invention. In particular, three-dimensional laser cuttingmachining is carried out using the nozzle, in which machining a cuttinggas is fed to the laser cutting nozzle at a pressure of between 8 and 23bar, and a metal profile having a workpiece thickness of from 1 to 4 mmis cut, at least intermittently, at a distance between the nozzle andthe workpiece surface that is in a distance range of between 3 and 6 mm.

In general, cutting is carried out at an angle of incidence of the beamon the workpiece surface of 90°. However, small contours can be cut forexample only using the pivot axes provided for oblique positioning ofthe cutting head, without using the translational axes; in this case,the contours can be cut at an oblique position of up to 30°.

Preferably nitrogen and/or compressed air is used as the cutting gas.

The dependent claims and the embodiments of the invention described inthe following relate to further configurations of the invention. Theinvention will be described in greater detail in the following, on thebasis of embodiments and with reference to the accompanying drawings. Inthe drawings, in detail:

DESCRIPTION OF DRAWINGS

FIG. 1 is a central cross-sectional view of a laser cutting nozzle,

FIG. 2 is a side view of the laser cutting nozzle according to FIG. 1,and

FIG. 3 shows a laser machining unit that comprises a laser cuttingnozzle according to FIG. 1 for three-dimensional workpiece machining.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a laser cutting nozzle 1 for a lasermachining unit. The nozzle 1 is a single-hole nozzle which is producedintegrally from copper. FIG. 1 is a central longitudinal section alongthe nozzle longitudinal axis 3. The nozzle 1 is substantially formed asa body that is rotationally symmetric with respect to the longitudinalaxis 2.

The nozzle 1 comprises a central passage 2 for a laser beam and cuttinggas, which passage extends from a nozzle inlet 4 as far as a nozzlemouth 5, along a passage longitudinal axis 6. The passage longitudinalaxis 6 coincides with the nozzle longitudinal axis 3.

The passage 2 consists of a cylindrical inflow portion 7, a continuouslyconverging convergence portion 8, and a divergence portion 9. Thepassage 2 has a circular cross section over the entire length L_(ges)thereof, i.e. over all the portions 7, 8, 9. The convergence portion 8transitions continuously, in an edgeless manner and gradually, into thedivergence portion 9 at a constriction 10.

In order to form an emergent gas flow that has ratios that arehomogenous and are favorable for laser melting cutting over a largedistance range of up to 6 mm, in the embodiment shown the passage 2 isformed in the following manner.

At the inflow portion 7, the passage 2 has a diameter d_(E) of 4.4 mm.At the constriction, the diameter d_(min) is 1.6 mm. The mouth dm′ has adiameter of 1.94 mm. Consequently, the cross-sectional area 11 at theconstriction 10 is less than 40% of the cross-sectional area 12 at theinlet 13 of the convergence portion 8 (corresponds to thecross-sectional area over the entire inflow portions since said portionis cylindrical). In particular, the constriction cross section 12 isonly 13% of the cross-sectional area 12 at the inlet 13 of theconvergence portion 8. By the mouth 5, the passage 2 has widenedcontinuously again to over 130%, in particular to 147%, of thecross-sectional area 11 at the constriction. The cross-sectional area 14of the mouth 5 is only 19% of the cross-sectional area 12 at the inlet14 of the passage 2.

In order to prevent the flow from “breaking off” in the edge region, thewall of the passage 2 is at an angle of inclination relative to thepassage longitudinal axis 6 of at most 5°, over the entire divergenceportion 9. The average angle of inclination α_(D) of the wall of thepassage relative to the passage longitudinal axis 6 in the divergenceportion 9 is 1.5°. In contrast, the average angle of inclination α_(D)of the wall of the passage relative to the passage longitudinal axis 6in the convergence portion 8 is significantly greater, at 12°.

The length L_(E) of the inflow portion 7 is 1.3 mm, the length L_(K) ofthe convergence portion 8 is 4.0 mm, and the length L_(D) of thedivergence portion 9 is 6.5 mm. The overall length L_(ges) of thepassage 2 is consequently 11.8 mm. The length L_(D) of the divergenceportion 9 is approximately 1.63 times the length L_(K) of theconvergence portion 8.

It is also significant that the length L_(D) of the divergence portion 9is less than 5 times the diameter d_(min) of the constriction 10. Inparticular, the length L_(D) is 4.1 times the constriction diameterd_(min).

The convergence portion 8 and the divergence portion 9 are not strictlyconical. The wall is curved towards the passage longitudinal axis 6 atleast in portions (convergence portion 8: radius of curvature of e.g. 6mm; divergence portion 9: radius of curvature of e.g. 26 mm).

The outside diameter d_(MA) of the nozzle 1 on the mouth side is 3.15mm. The width of the end face 15 extending perpendicularly to thepassage longitudinal axis 6, which face annularly surrounds the mouth 5,is 0.605 mm. This makes it possible to achieve a sufficiently highresponse characteristic for capacitive distance control that also allowsfor distance control in the range of up to 6 mm. Machining at a greaterworking distance increases the process reliability, with the result thaterror-free machining can be carried out at high speeds, at a feed ratein the range of 10-50 m/min.

Further details of the outer contour of the nozzle 1 will be explainedwith reference to FIG. 2, which is a side view of the laser cuttingnozzle 1.

A conical peripheral surface 16 having a length L_(KON) of 4.5 mm and anangle of inclination α_(KON) relative to the passage longitudinal axis 6of 28° adjoins the end face 15 on the mouth side. Approximately at theheight of the constriction 10, the conical peripheral surface 16transitions into a cylindrical peripheral surface 17, the largestoutside diameter d_(max) of which is 8.0 mm. The cylindrical peripheralsurface 17 is provided with a knurling 18 which functions as a grippingelement during handling, e.g. when screwing the nozzle 1 into a nozzlereceptacle of a machining head. An external thread 19 is formed on theperipheral surface of the nozzle 1, by means of which thread the nozzlecan be screwed into a nozzle receptacle of a machining head of a lasermachining unit for example.

The laser cutting nozzle 1 according to FIG. 1 is a preferred embodimentof a laser cutting nozzle 1 for three-dimensional laser cuttingmachining of metal profiles. The shaping of the passage 2 brings aboutdistance-independent, constant fluid dynamic radios at the workpiecesurface and in the cutting gap. The shaping of the outer contour ischaracterized by favorable characteristics for capacitive distancecontrol of the nozzle-workpiece distance.

The parameters of further preferred embodiments of a laser cuttingnozzle are set out in Table 1, together with the correspondingparameters of the nozzle 1 according to FIG. 1, all the example nozzlescoinciding at least with respect to the overall length L_(ges), theinside (d_(E)) and outside diameter on the inlet side, the lengthsL_(E), L_(K), L_(D) of the inflow, convergence and divergence portion 7,8, 9, the maximum outside diameter d_(max), and the length L_(KON) ofthe conical peripheral surface 16.

TABLE V Parameters of a plurality of embodiments of laser cuttingnozzles. d_(MI) d_(MA) d_(min) α_(D) α_(KON) α_(K) L_(D)/ d_(MI) ²/d_(MI) ²/ d_(min) ²/ No. [mm] [mm] [mm] [°] [°] [°] d_(min) d_(min) ²d_(E) ² d_(E) ² 1 1.94 3.15 1.6 1.5 28 12 4.1 19% 147% 13% 2 2.352 3.151.8 2.4 28 11 3.6 29% 171% 17% 3 2.855 4.15 2 3.8 23 10 3.3 42% 204% 21%4 3.398 4.15 2.6 3.5 23 8 2.5 60% 171% 35% 5 3.7 4.5 2.6 4.8 21 8 2.571% 203% 35%Example No. 1 corresponds to the nozzle according to FIG. 1.

FIG. 3 shows a laser machining unit 20 comprising a laser cutting nozzle1 according to one of the above examples. The laser machining unit 20comprises a machining head 21 that is equipped with a laser cuttingnozzle 1 and is intended for three-dimensional laser cutting machining.A laser diode, CO₂ or solid-state laser (not shown in greater detail),in particular a disc laser, having a maximum power of at least 2 kW, isused as the laser source.

The unit 21 has capacitive distance control of the nozzle-workpiecedistance.

The unit 21 for example carries out three-dimensional laser cuttingmachining using the nozzle 1, during which machining a cutting gas (e.g.nitrogen or argon) is fed at a pressure of between 8 and 23 bar. A metalprofile 22 having a workpiece thickness of from 1 to 4 mm is cut, atleast intermittently, at a distance between the nozzle 1 and theworkpiece surface that is in a distance range of between 3 and 6 mm.

For example, construction steel and stainless steel having a sheetthickness of 1 mm is cut at 50 m/min using a laser source at a power of5 kW.

What is claimed is:
 1. A laser cutting nozzle for a laser machiningunit, the laser cutting nozzle comprising: a passage for a laser beamand a gas, the passage extending between a nozzle inlet and a nozzlemouth along a passage longitudinal axis, the passage convergingcontinuously towards the nozzle mouth thereof, in a convergence portion,to a constriction of the passage, to less than 40% of a cross-sectionalarea at an inlet of the convergence portion, the passage divergingcontinuously in a divergence portion, proceeding from the constrictionof the passage, as far as the mouth of the passage, to over 130% of across-sectional area at the constriction of the passage, theconstriction of the passage comprising a point at which the convergenceportion and the divergence portion meet such that the convergenceportion transitions directly into the divergence portion at the point ofthe constriction; wherein, in the entire divergence portion, the wall ofthe passage is at an angle of inclination relative to the passagelongitudinal axis of at most 5°, and the length of the divergenceportion is less than 5 times the diameter of the constriction; andwherein the divergence portion has a length that is more than 1.4 timesand less than 1.7 times the length of the convergence portion.
 2. Thelaser cutting nozzle of claim 1, wherein the angle of inclination of thewall of the passage relative to the passage longitudinal axis in theconvergence portion is greater than 7° and less than 13°.
 3. The lasercutting nozzle of claim 1, wherein the angle of inclination of the wallof the passage relative to the passage longitudinal axis in thedivergence portion is less than 2.0° and greater than 1.0°.
 4. The lasercutting nozzle of claim 1, wherein the convergence portion transitionsin an edgeless manner into the divergence portion at the constriction.5. The laser cutting nozzle of claim 1, wherein the passage additionallycomprises a cylindrical inflow portion that is arranged upstream of thedivergence portion, on an inlet side.
 6. The laser cutting nozzle ofclaim 1, wherein the length of the divergence portion is less than 3times the diameter of the constriction and is more than twice thediameter of the constriction.
 7. The laser cutting nozzle of claim 1,wherein the cross-sectional area of the mouth is more than 180% and lessthan 220% of the cross-sectional area of the constriction.
 8. The lasercutting nozzle of claim 1, wherein the wall of the passage in theconvergence portion is curved towards the passage longitudinal axis, atleast in portions, which wall has a radius of curvature of between 4 and8 mm.
 9. The laser cutting nozzle of claim 1, wherein the wall of thepassage in the divergence portion is curved towards the passagelongitudinal axis, at least in portions, which wall has a radius ofcurvature of between 20 and 30 mm.
 10. The laser cutting nozzle of claim1, wherein the diameter of the mouth is between 1.8 and 3.5 mm, thediameter of the constriction is between 1.3 and 3.0 mm, the length ofthe convergence portion is between 3.5 and 4.5 mm, the length of thedivergence portion is between 5.0 and 7.0 mm, and the outside diameterof the nozzle on a mouth side is between 3.0 and 5 mm.
 11. The lasercutting nozzle of claim 1, wherein the nozzle comprises a conicalperipheral surface on a mouth side that is tapered toward an end face ofthe cutting nozzle at the mouth and that has a length of between 4.0 and5.0 mm and is at an angle of inclination relative to the passagelongitudinal axis of between 20° and 30°.
 12. The laser cutting nozzleof claim 1, wherein the nozzle comprises an end face that extendsperpendicularly to the passage longitudinal axis, annularly surroundsthe mouth, and has a width of between 0.3 and 0.7 mm.
 13. A lasermachining unit comprising: a machining head; and the laser cuttingnozzle of claim 1 secured to the machining head.
 14. The laser machiningunit of claim 13, further comprising a capacitive distance control ofthe nozzle-workpiece distance that determines the capacitance betweenthe nozzle and the workpiece for the purpose of the control.
 15. Thelaser machining unit of claim 13, wherein the laser cutting nozzle ismovable to perform three-dimensional laser cutting machining.
 16. Thelaser machining unit of claim 13, further comprising a laser source, thelaser source comprising at least one of a laser diode, a CO2 laser, asolid-state laser, and a disc laser, the laser source having a maximumpower of at least 2 kW.
 17. The laser machining unit of claim 13,wherein a laser source of the unit can generate a laser beam having abeam parameter product of less than or equal to 2 mm mrad.
 18. A methodof performing three-dimensional cutting machining on a metal profile,the method comprising: feeding a gas to a laser cutting nozzle, thelaser cutting nozzle comprising a passage for a laser beam and the gas,the passage extending between a nozzle inlet and a nozzle mouth along apassage longitudinal axis, the passage converging continuously towardsthe nozzle mouth thereof, in a convergence portion, to a constriction ofthe passage, to less than 40% of a cross-sectional area at an inlet ofthe convergence portion, the passage diverging continuously in adivergence portion, proceeding from the constriction of the passage, asfar as the mouth of the passage, to over 130% of a cross-sectional areaat the constriction of the passage, the constriction of the passagecomprising a point at which the convergence portion and the divergenceportion meet, wherein, in the entire divergence portion, the wall of thepassage is at an angle of inclination relative to the passagelongitudinal axis of at most 5°, and the length of the divergenceportion is less than 5 times the diameter of the constriction, whereinthe gas is fed on an inlet side, at a pressure of between 8 and 23 bar;and cutting, at least intermittently, the metal profile at a distancebetween the nozzle and a workpiece surface that is in a distance rangeof between 2 and 6 mm; wherein the metal profile has a workpiecethickness of between 1 to 4 mm; and wherein the divergence portion has alength that is more than 1.4 times and less than 1.7 times the length ofthe convergence portion.
 19. The laser cutting nozzle of claim 1,wherein the convergence portion and the divergence portion meet at theconstriction absent a cylindrical portion of constant diameter betweenthe convergence portion and the divergence portion.